1. Field of the Invention
The present invention relates to a method of and an apparatus for generating a color conversion table which converts color data to be processed by a first device into color data to be processed by a second device, and an apparatus for generating a proof using such a color conversion table.
2. Description of the Related Art
In order to produce desired printed materials of color images, it is necessary to take into account various printing conditions including the type of inks used, the printing sheets used, the illumination with which to observe the printed materials, etc. Desired printing conditions could be established by actually printing color images under various possible printing conditions. However, it would be unrealistic to produce test prints under all combinations of possible printing conditions because such test prints would incur an unduly expenditure of time and money.
There has been developed a printing proof generating apparatus capable of easily simulating the finished state of a printed material without actually producing the printed material. The printing proof generating apparatus operates by converting image data to be printed under various printing conditions to generate device-independent colorimetric data of colors expected of the final printed material, thereafter converting the calorimetric data into proof image data taking into account the characteristics of the printing proof generating apparatus, and then generating a proof based on the proof image data.
Since printing conditions can freely be established using a conversion table which converts image data into colorimetric data, it is possible to generate a proof easily and inexpensively and then to determine printing conditions under which to produce the desired printed material from the generated proof.
All colors of a color printed material can theoretically be produced from three colors of C (cyan), M (magenta), and Y (yellow). However, inks of these three colors may not necessarily have ideal spectral characteristics. In order to eliminate such a drawback, color printed materials are usually produced using inks of four colors which include the above three colors and an additional color of K (black). The printing proof generating apparatus also uses such four colors of C, M, Y, K for producing more accurate proofs.
A printed material and a proof thereof may colorimetrically be equivalent to each other, but may not necessarily be in sufficient agreement to the eye of an observer. Most typically, when a printed material composed of halftone dots is formed using only an ink of K, if a proof thereof is produced using a combination of inks of C, M, Y that are colorimetrically equivalent to the printed material, then the proof may possibly appear appreciably different from the printed material to the observer when observed microscopically. According to another example, while a printed material is formed using an ink of Y, a proof thereof may contain an ink of M in addition to the ink of Y. In addition, a printed material and a proof thereof, though colorimetrically equivalent to each other, may possibly be observed differently from each other if their halftone dot area percentages differ from each other. Such discrepancies manifest themselves in highlights and shadows of the image. The same problem arises if the dot gains of the printed material and the proof differ from each other.